Members' Online Book: Battery Installation & Maintenance, Chapter 1 of 18

Introduction—Defining The Problem


First off, let’s take a look at how this project, which resulted in this Online Book, started.

About eight years ago, we switched to Absorbed Glass Mat (AGM) batteries on Morgan’s Cloud, to get the following benefits over liquid filled lead-acid batteries:

  • Shorter recharge times since AGM batteries accept a faster charge rate.
  • No risk of the batteries freezing when we lay-up the boat unattended since AGM batteries have a very low self-discharge rate. (A fully charged battery won’t freeze but a flat one will.)
  • About 10% more capacity in the same size battery.

However, our experience with AGM batteries was not good: We went through four sets of house batteries from two different manufacturers after the switch to AGM. When you consider that AGM batteries are as much as double the price of liquid filled batteries, that stung.

In the process of solving that problem, we learnt a huge amount that can be applied to the care of any lead-acid battery. 

Hard Usage

We should state at this point that we are tough on batteries. At anchor, when we are usually writing and working on photographs, we use as much as 300 amp hours at 12 volts (3.6 kWh) per day for lighting and computers and about the same on passage what with the autopilot, navigation electronics, and lights.

And to make matters worse, due to space constraints, our house bank only totals 510 amp hours—about half the ideal size, given our usage.

In fact, it is likely that our bad experience with AGM batteries had little to do with our change to that technology, since said change coincided with a huge increase in our electricity usage due to the demands of this web site.

We Did The Right Things

However, although our usage is tough, we were doing all the things that are supposed to preserve batteries:

  • We never discharged our batteries more than 50%.
  • We installed chargers and a regulator that have temperature sensors and purport to be designed to properly charge AGM batteries.
  • We always recharged to at least 85%.

But, even so, the last set of AGM batteries died after less than a year and so we had pretty much decided to go back to liquid filled batteries. However, before we did that, we wrote to the manufacturer stating our concerns. What a pleasant surprise to get a helpful and concerned email from Justin Godber of Lifeline Batteries. A big contrast to the usual blow off or, worse yet, dead silence that we are used to getting when we complain about gear that has not met our needs.

The Plan

So we cut a deal with Justin: He provided us with a new set of AGM batteries for free and committed to advising us on their care and feeding. Our part was to write about the experience and develop a real-world set of recommendations, a manual if you will, on the use and care of lead-acid batteries on a voyaging boat.

This Online Book is the result. We also received a huge amount of wisdom in the form of comments to the original posts, which we have incorporated into this Second Edition.

The Problem

As we conducted a technical and detailed email exchange with Justin to try and figure out what had killed our batteries so early and how to avoid it happening again, it soon became apparent that we liveaboard voyagers are set up to fail as caretakers of any lead-acid batteries, not just AGMs, for the following reasons:

  • The yachting press and most battery experts have told us that you should not equalize AGM batteries. Wrong—any lead-acid battery of any type will sulfate with typical liveaboard use and eventually fail if you don’t get rid of that sulfation regularly with equalization. So, if you can’t equalize a battery, it does not belong on a voyaging boat.
  • Many, perhaps most, chargers and alternator voltage regulators are programmed incorrectly as they come from the factory.
  • Many chargers simply don’t behave the way they say they do in their own brochures and manuals—yes, even the fancy three stage ones.


Worse still, the general instruction from manufacturers and battery experts, that all you need to do to enjoy a long life from lead-acid batteries is to fully charge them after every discharge, is completely impractical. Here’s why, based on our own installation, but the fundamentals will be the same for any boat: It takes two hours of generator or one hour of main engine time on Morgan’s Cloud to bring our house bank from a 50% discharge state to a 85% charge, but four more hours of charging to get from 85% to 100%.

This same basic fact will apply no matter how powerful your charging source is since the limiting factor is the amount of current (amps) that a battery can accept for the last 20% of its charge cycle.

So this “standard wisdom” is fine if you are in a marina and can plug in, but totally impractical on a voyaging sailboat that may not see shorepower for months at a time and that discharges the batteries by 50% on most days at anchor or at sea, since no one in their right mind is going to run a main engine or generator lightly loaded for five to six hours a day to reach full charge.

What’s Full Charge?

Before we go any further, it is vital that we clearly define what full charge is and how to measure it. Read this carefully because understanding this one fact is vital to managing batteries:

A lead-acid battery is fully charged when the current (amps) it will accept at its specified acceptance voltage—typically about 14.4 volts at 70F (20C)—has dropped to 1-2% of the total capacity measured in amp hours. This is the only practical way to know that a battery is charged. 

Amp counters, voltage measurement at rest, and other methods are approximations at best and, if you rely on them, you will almost certainly get less life out of your battery than it’s capable of supplying. The only way to accurately measure charge amps is to have an amp meter with a shunt on the positive side of the battery. More on that later.

Alternative Energy

Before we go any further, it is important to mention that wind and/or solar power can help to bring your batteries up to full charge every day. But only if you have enough charging capacity to both supply your needs during the day and replace whatever you took out of the battery the night before. That’s a lot of alternative energy, the installation of which will often result in an unseamanlike festooning of the boat with solar panels and wind generator(s). To learn more about alternative energy read Colin’s excellent Online Book Alternative Energy for Voyaging Sailboats.

Real World Tested

But even if you do have that much alternative energy generation capability, applying the techniques you will learn from reading this book will make your batteries last even longer. We know this because we are now getting great service from our batteries, even with our brutal use and undersized house bank.


Justin bought one of my prints for his office wall and he, as stated above, provided two 8D AGM batteries at no cost to us. Those are the only benefits we have received from Lifeline Batteries.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

50 comments … add one
  • Robert Aug 2, 2010, 2:05 pm

    A known way to charge the battery close to 100% at each cycle without much trouble: split the battery into two separate banks. Each bank is used only every two days and the other bank is charged close to 100% during its “rest day” with solar, wind, engine or generator without increasing much the overall generator working time.

    • John Aug 3, 2010, 6:52 am

      Very good point. The only trouble is that to do that, and still not cycle our batteries deeper than 50%, we would need to double the size of the battery bank, something we don’t have the space to do. Also, if we did double the size of the bank, we might be better served by using the whole bank and only discharging to 25%.

      Finally, if we only charged half the bank at a time, we would not be able to fully load the generator since only half the bank would be in high absorbing mode.

      Having said that, the system you propose might work great for a boat with lower power requirements than ours and with lots of solar and wind power. It would require some fairly complex wiring to route the charging current to the resting battery while making sure that it did not see any loads.

    • Matt Boney Nov 26, 2013, 10:37 am

      I think Robert’s advice on splitting battery banks, and maybe not having a starter battery, does not match with current thinking in that it is much more efficient to have just one large service bank and a much smaller starter battery.
      There are 4 very good reasons why bigger is better:

      1. Doubling the service bank size means the life cycle is longer as the DoD is unlikely to fall so close to 50% so often. Life cycle at 50% DoD may be 1000 charge and discharge cycles. At a DoD of only 25% the life cycle may be 2500 or more. vs Life

      2. Doubling the service bank size also means the “apparent capacity” is greater. Peukert’s law says that the apparent Ah size of a bank changes depending on the current draw.

      A bank is designed to deliver a capacity with a current discharge that will flatten the battery in 20 hours. (The 20 hour rate) So with a 100Ah battery, a 5A load will flatten the battery to 10.5v in 20 hours.

      When drawing currents higher than 5 amps the “actual” bank size will be much smaller, so the bank will not last as long before it needs re-charging. Conversely when using much less than 5 amps the bank size will be larger and will deliver more Ah.

      If a 100 Ah that battery has a Peukert value of 1.25, then higher or lower loads than 5 amps will change the actual capacity of the battery by the following amounts.

      With a 10A load for 20 hours there are only 84Ah’s in the 100 Ah bank.

      With a 1A load for 20 hours there are 150Ah’s in the 100 Ah bank.

      3. Doubling the service bank size also means it will be more efficient and accept more Ah more quickly from all charging sources during the boost phase up to 80%.

      It takes a bit of very over-simplified maths to prove the point, but a 100 Ah battery that is discharged to 50% may accept 20Ah in the first hour during the boosts stage, maybe 10Ah in the second hour during the start of the less efficient absorption phase, and the remaining 20Ah in another 5 hour. Doubling the battery size to 200Ah, with the same charging source of 20 amps, will accept 10Ah into each battery in 1 hour, that’s 20Ah into the bank. In the second hours it will store another 20Ah. That’s 40Ah replaced in two hours, as compared to 30Ah with a single bank. In the 3rd hour it may still accept 20 amps into the bank because a single battery in the start of the absorption phase could accept 10 amps. That’s 60Ah in three hours.The key point is that for two hours it is still in the more efficient boost stage where the battery is taking all the current the charge source can give it. Note that the initial boost charging stage has captured 40Ah in two hours, and 60 Ah in three hours. With the smaller bank it could only capture 20Ah in the first hour during boost and 30Ah after the second hour during the start of absorption. The third hour may add another 5 amps. That’s 35Ah with one batteries and 60Ah with two batteries. So a bigger bank will be more efficient and accept more Ah more quickly from all charging sources.

      Since a lot of the time we are only charging up to the absorption stage which is about 80-85% then this increase in stored Ah is significant.

      4. If you have a larger bank – or many smaller batteries in one large bank, it is easy when they start failing to just disconnect the bad ones and run on the others as long as you can until you can replace the whole bank. This may also allow skippers to search around and find the batteries they really want – not just be forced to buy the local “rubbish” because they are desperate.

      • John Nov 26, 2013, 11:48 am

        Hi Matt,

        All good points that I would agree with. However, there are also advantages to splitting into two banks too:

        • Allows you to use one bank while equalizing the other.
        • Allows you to fully charge the unused bank using say solar while the other bank is being used. The result is that with adequate solar each bank gets brought up to 100% every other day. And charging to 100% frequently is the single most important thing you can do to increase battery longevity.

        So, like so many things in voyaging the answer to which is best, one bank or two—I’m talking about splitting the house bank here, since I believe the engine start should always be separate from house—is that oh so unsatisfying “it depends”.

        For me, I like to have the house bank split because it gives me the best of both worlds since most of the time I leave the switch that splits them on “both”, to get the advantages you explain so well, but when it makes sense I can split them up, say when equalizing.

        • Matt Boney Nov 26, 2013, 12:03 pm

          A switch to split when you need to is a very good solution for equalizing. I just EQ one at a time by disconnecting the others. I think the advantages from the Peukert effect of having effectively a much larger bank means the batteries will last much longer. I have only 140 watts of solar that supplies the daily needs, and 400W wind. We have to find some shorepower every 3 weeks to get the bats to 100% – in between the 280 A DC genny and the motoring which we seem to do a lot of here in the med. My 1050 Ah Lifelines are now in their 10th year and standing up very well to individual 10 hour load tests right now. I only EQ them at the beginning and end of the season.

  • Matt Marsh Aug 3, 2010, 8:23 am

    I’m as surprised as you were, John, that your AGMs would be dying so quickly. Hopefully your experiments will reveal the cause of the problem- I’m betting on charger programming, but that’s far from the only possibility.

    More sophisticated batteries inevitably bring with them more potential problems and the need for more advanced monitoring systems. Taken to the extreme, this results in the lithium polymer battery packs we used to use on solar cars, and that have now evolved for modern electric cars: 5 kWh or so from a 30 kg battery (the equivalent of over 400 amp-hours at 12 V), but each string in the pack needed real-time monitoring for over-voltage, under-voltage, over-current and over-temperature- any of which could result in either a string failure or a cell breach.

    One thing that those Li-Poly experiences taught me was that, whenever possible, it’s best to obtain protection and charging circuitry from the same engineering team that designed the battery. If that’s not possible, then the different suppliers have to be willing to work together and provide each other with detailed specifications and all the characterization curves for their respective products. The battery guy, for example, should be able to give the charger guy a book of graphs relating voltage, state of charge, input or output current, charge acceptance rate, etc. for all foreseeable operating conditions.

    • John Aug 3, 2010, 3:23 pm

      You are absolutely right. As you will see as the series unfolds, the big problem is that the battery and charger manufacturers, in the marine business, are not on the same page.

  • Robert Aug 3, 2010, 11:40 am

    I have a friend living on his sailboat without shore power for several years. Only Solar panels and diesel generator. He uses standard industrial positive tubular motive power batteries, with two banks as previously mentioned, one day rest and 100% charged, one day in use and partially charged. After 7 years and about 1300 cycles, these batteries contain still about 70% of the initial Ah value.

    The life time of this type of industrial batteries (2 volts elements) is about 1500 cycles at 50% discharge and C/5 discharge current, or 10 years floating. Their cost is much lower than AGM or gel batteries. About 1.5 – 2€ per Ah at 12 volt. (there are many other manufacturers)

    • John Aug 3, 2010, 3:20 pm

      Thanks for the really good real world data. I’m sure it will be really useful to our readers.

      Unless I’m missing something, this system requires a battery bank total capacity of four times daily use? That is unless the user is willing to run the generator more than once a day. For boats that can fit that number of batteries in, it would seem one of the best systems.

      There is one other point: Most generators run at constant RPM and near constant fuel burn, regardless of load, therefore such a system will only be fuel efficient if the generator is sized to be fully loaded when charging half the bank (plus other loads) in absorb mode. Since the smallest diesel generators are around 5Kw this would, once again, imply about a 1000 amp hour battery bank at minimum. The other option would be a small gas generator, like the Hondas, or one of the newer technology variable RPM generators.

      All of the above shows the importance of a total systems approach in all of this.

  • Alan Teale Aug 9, 2010, 3:11 pm

    For one expert’s rather sobering comparison of battery types see

    Your boat may not resemble that on the web page, but I don’t think that is relevant.

    • John Aug 9, 2010, 3:34 pm

      Thanks for the pointer. A good article, albeit a bit simplistic, at least in my opinion. He does start with one wrong piece of information though and that is the relative cost of gel batteries. Our research has shown that gels are generally cheaper than AGM, not more expensive. Also, good quality heavy duty liquid batteries are generally more expensive than the number he bases his case on.

      He is just plain wrong in his assertions about the fast charge rate of AGM batteries resulting in liquid loss and gassing. Actually, the exact opposite is true: AGM batteries, if not overcharged, gas much less than liquid batteries.

      One other point, he is in England, where it does not often freeze hard. One of the big benefits for us of using AGM batteries is that we can leave Morgan’s Cloud laid up for months in temperatures down to -30c without having to worry about the batteries freezing due to self discharge.

      Having said all that, I think that his basic premise that liquid batteries are by far the best value is indisputable. However, there may be compelling reasons to use AGMs that his overly simplistic analysis misses. Bottom line, I’m always skeptical of any article that claims to have the definitive answer for all of us.

      • Matt Boney Nov 26, 2013, 10:22 am

        This a very very old and much criticised article from a man who is a law unto himself!!! I don’t think this character does himself (or his products) any favours by still publishing an article so full of glaring errors and contradictions.

        The truth of the matter is his earlier chargers were not “sealed battery friendly ”. Basically when the charger dropped down to float mode they were not offering truly adaptive charging in that they did not provide a proper maintenance current to feed domestic supplies. If the load was too high, even though the batteries were fully charged, the charger would go back into the full charge cycle which means back up to around 14.4 volts and hold this absorption voltage before it eventually fell back to float. If it did this too often for too long then the batteries would gas too much and sealed batteries would die prematurely. This was corrected in about 2009 with his “powerpack” function that provided the full charger output load in float condition. He lost a lot of friends with this basic mistake.

        • John Nov 26, 2013, 11:36 am

          Hi Matt,

          You are absolutely right. (I was trying to be kind.) I have an chapter about what you are referring to here.

          • Alan Teale Nov 27, 2013, 9:45 am

            Thank you John and Matt. That was helpful and enlightening. Alan

  • Alan Teale Aug 10, 2010, 9:12 am

    I think the point made in the Sterling Power article about gas and liquid loss on charging is that gas and liquid loss are not a problem with so-called sealed batteries or VRLA’s (AGM and Gel for example) precisely because they are, or should be, charged less aggressively than wet cells. And for this reason I am not sure why folk think that fast charging is a great feature of AGM’s. I do realize that there is some recycling of gas in AGMs, which mitigates the problem to a small degree.

    May I ask if self discharge were not a major consideration for you, would you still favour AGMs?

    And do you think the risk of spills and/or hydrogen production rules out wet cells on small sea-going vessels?

    • John Aug 10, 2010, 11:53 am

      With respect, I still think that you and the author of the article have it backwards. I have it on very good authority, and backed up by my 8 years of living with AGM batteries, that the whole point about AGM batteries is that they accept a higher charge rate than liquid cells without gassing. In fact AGM batteries actually like to be charged at their full acceptance as long as the voltage does not go over a nominal 14.4 Volts (at 70f). Note that to do this safely, the charger needs to be temperature compensated so that the voltage is dropped as the battery temperature increases.

      In fact this is true of all lead acid batteries. The idea that charging slowly (below the battery’s maximum acceptance) is beneficial is one of the most persistent myths in battery care.

      To answer your questions:

      On balance, if self discharge were not a problem with liquid acid batteries I think that I would go that way because of the lower cost and the fact that if you do make a charging error (over voltage) and boil off liquid you can add more. But it would be a close run thing. When you have the capability to generate 150 amps plus of charge current in two different ways, as we do, it is really nice to have AGM batteries that can accept that for about 85% of their charge cycle, thereby lowering your generator or main engine run time.

      And no, I have no problem with liquid batteries on an offshore boat. Batteries should be properly secured and vented anyway, whatever technology they use.

  • Justin Godber Aug 10, 2010, 2:49 pm

    Hello All,

    I am Justin Godber with Lifeline Batteries. I have been working with John and following this blog. I thought I would start by responding to some of the topics above and clarifying a few things and answer some of the questions that will follow.

    AGM batteries ARE a lead acid battery. So are GEL batteries. They all just contain the electrolyte in different ways. There are three types of lead acid batteries: Wet Cell batteries, GEL Cell batteries and AGM batteries.
    Wet cell batteries as we all know are the type that you have to refill with water. They are messy and can be more dangerous because of the volume of hydrogen that is emitted during recharge.
    GEL batteries have taken wet electrolyte mixed with silica sand to make a GEL. We used to make these until about 1989. As most people think this is a “newer technology”, really it is quite old and as I stated we actually stopped making these in 1989. GEL batteries are sealed and work well with very strict charging regimes. The biggest problem with GEL batteries is the charging and the vibration. With vibration the GEL forms all these small air bubbles. Similar to what you would see in a bottle of hair gel. These air bubbles virtually cannot go anywhere so they stay in the GEL. All is fine until all these bubbles sit against the battery plate. Any and all bubbles that are against the plate will not be able to produce any capacity because there is air there, not electrolyte. This may not sound like a big deal but there could be thousands of bubbles in there covering more than 50% of the plates. Secondly, the charging. Charging GEL batteries can be very temperamental. GEL batteries require very strict charging voltages and cannot really deviate 1/10 of a volt either way to avoid premature death.
    AGM Batteries. This is important. NOT ALL AGM BATTERIES ARE CREATED EQUAL. AGM batteries have all the electrolyte absorbed into a fiberglass matting. They are then charged and formed and then all the excess acid is dumped out. We then seal the caps on the battery permanently. This results in a completely sealed battery. You can charge these batteries with 100% of their amp hour rating. This is a big advantage. You can charge a 100 amp battery with 100 amps. In fact they actually respond better in lab conditions when they are charged up faster. A Wet cell and GEL cell can only take 35% of their rated capacity on recharge. Making an AGM battery is like making a cake. The recipe has to be just right. We take pride in our batteries, we make everything (proudly) in the USA, and I mean everything. We also manufacture everything by hand. We have 17 quality checks as we are going down the line. We make batteries for Marine, RV, Aircraft, and Solar industries. We make a true deep cycle battery for the marine industry. Besides being very expensive to manufacture we really have no cons over any of the aforementioned battery types.

    Now that all battery types have been explained, here is the part you have been waiting for. ALL batteries need to be fully recharged to avoid sulfation build up on the plates. I am not sure if I can post links on here so before I do I am asking. I can send links for Trojan Battery, Deka Battery, Odyssey Batteries, etc…They all state the same thing. Batteries must be fully recharged to avoid damage and premature failure. This is why:
    As I mentioned before these are all lead acid batteries. They all perform the same chemically when charging and discharging. These batteries are all made from lead and lead dioxide and electrolyte. When the battery is discharged the plates go under a chemical reaction called lead sulfate. When the batteries are recharged this reaction is reversed. This reversal changes the plates from lead sulfate back to lead and lead dioxide. When the batteries are left to sit in a discharged state the lead sulfate does not get reversed and starts to harden, or crystallize. When you look at it under a microscope it looks like crystals. The longer it sits like that the harder it gets and slowly starts to grow farther around the plates. This is the part where I will tell you how sailors eventually ruin batteries.

    Trust me, if I was in most of your positions I would probably do the same thing even knowing what I know. Batteries are not like a fuel tank. You cannot refill them to 85% and expect to always have 85%. As I stated the hardened sulfate will start growing. So when you use the 50-85 rule it works great for the first six months and then as the resistance starts to build and the sulfate starts to grow it goes 50-84 and then 50-83 and then 50-82 etc…Even though your charger says you are back to 85% it doesn’t really know because the resistance starts confusing the charger. It thinks it is back to 85% when it is slowly deteriorating. Eventually you will not be able to get the batteries above 12.2 volts and then we get a phone call.

    There are a few solutions to avoiding this scenario. The easiest one for us, but not for you, is fully recharging every time. This will keep the batteries healthy all their life.
    The other scenario when cruising is to use the 50-85 rule but you must equalize your battery bank once or twice a month. This will stop the sulfate from hardening as much as it would normally. John is currently using a similar scenario as field and we have had success in the past with some Trans-Atlantic crossings and they end up on the other side of the pond with fully charged batteries.
    That last paragraph will bring up the next question. “I thought you couldn’t equalize AGM batteries”. Well, as I stated earlier ALL AGM BATTERIES ARE NOT CREATED EQUAL. I can only speak for our batteries but you can equalize them. It is a great tool to use on the aforementioned scenario. Also a great tool just in general to help clean off the plates and gain some capacity back.
    Sailors have always struggled with all this battery/battery charging and we know why. We also know why you will only charge to 85%. As I stated I probably would do the same thing but we have been working and simulating your scenarios in the lab for years and we think the program that John is on is going to be successful.

    I want to write so much more but I will wait for questions, concerns and comments so I can be more specific.

    -Justin Godber
    Lifeline Batteries

  • molly mulhern Aug 11, 2010, 10:41 am

    Could someone give me a two-sentence explanation of equalization for an AGM battery? (what it is and how it is done?)

  • John Aug 12, 2010, 12:01 pm

    Hi Molly, Sorry, I should have defined my terms.

    Equalization or conditioning—strictly they are different, but we are going for brevity here—is a process where a fully charged battery is intentionally subjected to a higher charge voltage than normal for a fixed period. The idea is to break down the sulfate crystals that form on the plates due to repeated under charging.

    We will be dealing with the “how it is done” bit in the next post.

  • Allan Aug 13, 2010, 10:36 am

    I have been researching replacement options for my 9 year old Surrette wet cell batteries, now in their last season as they no longer hold a charge and after weeks of research one thing I have concluded is that it is not simply a matter of replacing my batteries but one of upgrading my entire electrical system. It seems obvious that AGM batteries are the way to go for me and for the same reasons that John and others point out…long cold winters, poorly vented confined spaces and the ability to bulk charge quickly. What I have learned from my research is that to use AGM technology to its max you must also consider upgrading your recharging and regulation methods accordingly. For us, cruising on our Bayfield 36 for extended periods has revealed that we are power misers when we need to be and also that we do motor at least half of the time due mostly to the sailing characteristics of the Bayfield as well as the prevailing winds here in Nova Scotia.
    The 44hp Yanmar onboard is equipped with a 55 amp alternator that only produces near its max output at 2800 rpm which is also the recommended max sustainable cruising revs, but for fuel economy we normally operate around the 2000 rpm range. All this to say that in addition to battery updates we are considering replacing our 55 amp alternator with a high temperature 120 amp alternator that produces 85% of its rated output at idle speeds! This is a huge plus when using high load applications such as a windlass or an inverter. Remember that if an AC appliance like a coffee maker draws 10 amps at 120 volts, then the DC draw on the battery bank will be 10 times the current or 100 amps. Having an alternator that can provide most of this draw for the short periods they are used will reduce the drain on the battery and hence a faster recovery when topping up the battery. I also believe that the smart regulators available today are ideal for our boat needs as they provide three levels of charging and will accept inputs from many sources including wind turbine, solar, generator and alternator. What remains to be settled for us is the selection of the components so that our preferred option AGM batteries are safely charged and have a long life cycle.

    • John Aug 13, 2010, 10:55 am

      You may wish to wait for our next post before you actually buy anything in the way of regulators or chargers.

      We have had some huge disappointments in that area over the last four years.

      Bottom line, a lot of this stuff just does not work as advertised.

      The offenders will be named.

  • Kettlewell Sep 24, 2010, 5:56 pm

    I’m in need of new batteries so these posts are very interesting. In the past I had a catamaran with no real engine charging, just solar and wind, and we had gel cells that were totally abused. They were discharged completely numerous times, charged without any sort of regulation, etc. and they were the longest lasting batteries I’ve ever had. I finally retired the original Sonnenschein’s after I think 10 years of use and abuse just because I was worried they would soon die, but they were still OK at that point. By the way, that boat sat over winter in Maine with a couple of solar panels hooked up and I never had a battery freeze, even when the snow covered the panels—it would eventually melt off. Subsequently, I have a different boat and went back to wet cell, deep-cycle batteries and they have routinely lasted about 3 years, which is exactly what I have found on numerous other boats. I have not owned Rolls, but in the past Surettes, and I couldn’t justify the price. Wet cells of almost any brand seem to last 3 years onboard and then fade rapidly. So, in recent years I buy whatever I can get cheapest. I’m now tempted to reconfigure to allow me to use cheap golf cart 6-volt batteries that can be obtained places like Sam’s Club because so many have reported such good success with them.

    • John Sep 25, 2010, 5:22 am

      Great input, thanks. I too have wondered about the 6 volt golf cart option, but did not know that they were so generally available. Sam’s Club, who knew? We would be really interested in knowing how that works for you if you decide to go that way.

      Also, we had really good service from Gells, in our case Prevailers. I have hesitated to draw too many conclusions from that because our usage was very different then, but still it is interesting. Perhaps Gells are not as fragile as generally thought? Anybody else have any experience, good or bad, with Gells?

      • Kettlewell Sep 25, 2010, 9:29 am

        Another thing I really like about the golf cart route is that you can actually lift each battery by yourself, facilitating the change out when you need to do it. Having struggled with 8Ds in the past, I find them just too unwieldy. My current set up uses a bunch of Group 31 12-volt batteries, which are liftable by a normal human. One the other side of the coin, if a battery dies when you are in some area away from civilization the chances of finding 6-volt golf cart batteries is not too good, but anywhere you find people you can find some sort of 12-volt battery. It may not be the ideal deep cycle, but it might be OK to help you limp along for awhile. I keep enough battery cable and fittings onboard to reconfigure my battery set up if I need to. Even a good set of jumper cables might help you out in a pinch.

  • Greg Oct 6, 2010, 1:52 pm

    I’m a marine electrician and a sailor, and have had similar experiences to yours in regards to AGM batteries, both with my own boat and with multiple customer boats. I think the marketing hype behind AGM batteries made a lot of people jump on the bandwagon, and they are a poor choice for most cruising boats. If you find a way to increase the unacceptably short lifespan for AGMs on cruising boats I will be very interested to find out how, but I have tried many so-called solutions with no success. Also, I’m glad to see Justin is working to help you. My interactions with him and with Lifeline in general were so dismal that I won’t ever do business with his company again.

    • John Oct 7, 2010, 7:50 am

      We had pretty much come to the same conclusion about AGM batteries for cruising boats. However, Justin (we have always found him helpful) convinced us to give them one more try.

      We should have some solid data on whether or not they will last, using the protocol we have worked out with Justin, in six months or so, but our initial findings are encouraging. However if they don’t go at least three years with our daily deep cycles, we will go back to liquid filled. Stay tuned.

  • Charles Freeman Nov 1, 2010, 6:40 am

    I use wet cells, but I am following the thread because your recommendations are going to apply equally well to wet cells – because they are ALL lead-acid batteries.

    I use Trojan T-105 6V batteries. I got seven years from my last set. I probably would have gotten another year or two, but had a knock-down that drained about half their acid out (successfully captured by my battery box, thank goodness) and by the time the passage was over they were toasted. However I am pretty hard on batteries – never equalized them in their entire seven years. (I will change that habit now, if I can – awfully hard to equalize batteries on wind and solar). There were a few years in the middle where we were CLODs and weekend sailors so the solar panel would bring them back to 100% during the week.

  • John Nov 1, 2010, 8:52 am

    On the life of an AGM in a constant full charge application: The starter battery on “Morgan’s Cloud” is a Lifeline 4D that is eight years old. Still turns the diesel great. That would seem to suggest that Justin is right about the whole problem with his batteries failing in a year or so being traced to undercharging.

  • Harvey Nov 11, 2011, 4:39 am

    After I had to replace on my Swedish Regina35 three 100AH LEOCH AGMs after only 3 years of useful life ( they are charged by a MASTERVOLT charging and monitoring system as well as a small solar charger), I spoke to a MasterVolt rep in the Bay Area, CA, about possible problems that may have lead to the batteries’ sudden death. He pointed out that often people don’t think to turn off the solar charger several hours before charging, which leads the controller to believe the batteries, showing higher voltage from the solar charger, are much fuller than they actually are, which leads to undercharging.
    Another issue was the fact that we had to leave our boat after a cruise without fully charging the batteries, so the solar charger had to trickle charge them over days, and a third reason seemed to be the setup of the cables, which weren’t at the terminals at opposite ends of the 3 batteries in parallel. In the end the LifeLine Dealer tested my Leochs and found one in pretty good condition (80% capacity), the others, interestingly the ones further away from the pos and neg terminals where the main cables were positioned, in pretty bad condition. My LifeLine rep said they had tested different setups of connecting batteries in parallel and found that charging and discharging characteristics were quite different depending on where you connect the main cables to the terminals. We will see what comes out of my new LifeLines I just installed 3 weeks ago.

    • John Nov 12, 2011, 1:00 pm

      My guess is that a very slightly poor joint at one of the cables, rather than the position of the cables themselves, was the culprit. A very small elevation in resistance caused by just a bit of corrosion will cause a surprisingly large difference in the charge voltage at each battery, and that in turn will result in the battery on the far side of the bad contact being constantly undercharged.

      A good test to prevent this is to discharge your batteries to say 50% and then check the voltage with a high quality digital meter, at the positive of each battery against the common ground point while the charger is on. A difference of over one tenth of a volt (.1) is a problem, and less than one twentieth (.05) is worth striving for by cleaning all the contacts.

      I don’t believe that the elevated voltage caused by solar charger is meaningful. Whether or not the battery will accept charge is a function of its own internal resistance, which is in turn, an indication of its charge level. The solar panel will charge it to whatever level it achieves when it is connected. When the AC charger comes online it will take it the rest of the way. In fact, it would make no difference to leave the solar panel charging in parallel with the AC charger. All of this assumes that both the AC charger and the solar panel are properly regulated and those regulators are sensing the voltage at the battery.

    • Chuck B Jul 1, 2016, 1:09 pm

      Hi Harvey, here’s an article that beautifully describes the problem with (and the solution to) the way your batteries were wired in parallel. This was an eye-opener for me!


  • Harvey Nov 12, 2011, 6:40 pm

    Thank you for your very helpful tip about checking the connections during a bulk charge for voltage differences to find problems with the cables, etc. I sure will make use of this with my new LifeLine batteries. Regarding your suspicion of a weak link in the cables, I don’t think this was the case because not only did I check the cables and connectors, they also were in a like new condition: no corrosion or layers whatsoever, tight connections at the screws as well, threads shiny and clean. I don’t really know what to say was the culprit if not the solar charger.

    • John Nov 12, 2011, 7:15 pm

      On the contacts, when you are dealing with low voltages and high currents (amps) just because they look nice and shiny, does not mean that they are without resistance. A contact that looks perfect can have just enough oxidation to cause enough resistance to unbalance the batteries. The only way to know is to measure with a high quality meter.

      On the varying opinions. Next time you are trying to decide on the veracity of an opinion, ask the person opining to quote ohms law and explain what it means in one clear sentence and how it should be applied to the problem at hand. I don’t mean to be facetious here, or arrogant, but the sad fact is that I would venture to guess that some 50% of the “professionals” in the marine electrical field would fail this test horribly. They simply don’t have the basic understanding of the underlying physics to adequately evaluate a theory about how to wire a boat. So what they do is take a popular myth and repeat it as fact to sound knowledgeable. That is why a good 50% of the “common wisdom” about batteries is just plain wrong.

      On the bright side, most all of this stuff can be explained and understood using high school physics. I was fortunate enough to have ohms law banged into my thick skull by a very dedicated teacher some 45 years ago.

  • Don NZ Dec 6, 2011, 7:15 pm

    I wonder if a more accurate test might be to apply a load say around 50 amp? Its value is not critical but its consistency is. Ever test using the same load while measuring the voltage?

    • John Dec 6, 2011, 8:55 pm

      I’m assuming you are talking of a discharge test?

      You are right that constancy is important, but having said that, you can get a reasonable idea with the protocol that we outline.

      At 50 amps test discharge rate on an 8D, you would get a much lower capacity reading since that would represent over 20% of the batteries capacity, not a level that one would, or should, use regularly for long periods.

  • JCFlander Feb 16, 2014, 11:38 am

    Hello John,

    Thanks for all the good work with this battery issue.
    Just a suggestion… for sake of completeness: how about adding an article about battery installation? It seems there’s plenty to think about…

    Some points:
    – How to connect the bank. Terminals cross-connected vs. end-connected.
    – How to connect when splitting the bank (e.g. SB/PS)
    – How to secure the bank. (Will single 1″ nylon strap with zinc/plastic lock do?)
    – How to vent outgassing when equalizing?
    – How to protect the bank from flooding with seawater during capsize?
    – How to keep moisture out of battery base? (if wet it will drain eventually, like on wet concrete floor)

    And some wet-cell specific:
    – How to keep outgassing sufuric acid fumes out of terminals?
    – How to keep acid in control when capsized upside down?
    – How to orient the batteries to prevent celltop exposure on heeling?
    – How to minimize water consumption (charger voltage/temp, water miser caps…)

    I think many of these points are already discussed on comments. It would be very good to have them collected in a single article.

    JC Flander

    • John Feb 16, 2014, 2:12 pm

      Yikes JC, that’s a carear! Seriously, some good ideas, I will add it to the editorial schedule. It may be some months before it sees the light of day, we have a large backlog. And to think I used to worry about running out of things to write about!

  • JCFlander Feb 16, 2014, 9:15 pm

    Hi, Thanks.
    That is a collection from many sources, including
    – Ed Sherman (ABYC,
    – Nigel Calder (we all know him, right?)
    – Steve D’Antonio articles on Professional Boatbuilder ( )
    – RC Collins blogs, like:
    – Alan Hugenot’ s whitepapers:
    – David Pascoe’s articles:

    All excellent men, who have seen the trouble to share their experience with others. Ofcourse with article fee, sometimes, but still… sharing our knowledge makes the world better for all of us. I think that that’s what I like most on Sharing makes a difference.

    …and also, some points collected from my own experience as Automation-engineer-come-boat-electrician.

    On the subject of battery bank installation – it is just amazing how many sailboats have lost all their electric power even after small flooding.
    There’s so much work to do to get this situation better. ABYC E-11 and ISO 10133 only define an absolute minimum baseline.
    That’s just not enough for boats offshore – even less on the high oceans.

    I try to collect and email you the complete reference list re. that battery installation thing.
    JC Flander

  • Clint Jun 17, 2014, 7:34 pm

    John, I have been living aboard for 12 years and have been fighting the battery life issue also. Two areas that I did not read about and have been pointed out to me as a possible problem with my install are:
    Use of both 4d and 8d batteries as part of one parallel 12volt house bank is not a good idea because the 8d’s never get fully charged?
    The other is regarding the cabling. I was told that the batteries would charge more uniformly if all the connecting cables were all the same length?

    • John Jun 18, 2014, 7:34 am

      Hi Clint,

      Testing at lifeline indicates that there is actually no problem with mixing batteries of different sizes, as long as they are of the same type and age.

      And yes, batteries in parallel will charge more evenly if the length of the cables from the charge source is same.

  • Chuck B Sep 13, 2016, 10:45 am

    Does anyone have experience with non-electric (i.e., hydraulic, spring, etc.) starter motors on a cruising boat? At first glance it appears to be a feasible way to eliminate the starter electrical system AND have a manual way to start the engine. I’m wondering how well that works out in practice.


    • Eric Klem Sep 13, 2016, 3:16 pm

      Hi Chuck,

      I have used a recoil (spring) starter before. They make a good backup but would be an incredible pain on a day to day basis and practically impossible to operate in some engine rooms. I have also used air start engines which are now pretty uncommon except for really big engines. These work okay but you need a compressor and associated plumbing which is just more stuff to break.

      To me, a well designed electrical system is pretty darn reliable for engine starting so I don’t worry about it. We have a battery whose only job is to start the engine if the house bank isn’t working for some reason. I have one time had a main battery switch break but that takes 2 minutes to bypass with a single wrench. I have also had starter solenoids seize up and starter contacts wear out. With the solenoid not working, a screwdriver across the terminals is exciting but effective at starting the engine. With the bad contacts, you can usually get it to start several more times by either hitting the starter with something or rolling the engine over. I believe that long distance cruisers should carry a backup starter and have either a backup alternator or a different way of recharging such as solar or wind (and a backup alternator is still a good idea then).


      • Chuck B Sep 14, 2016, 10:36 am

        Thank you Eric for sharing your experience. Guess it’s not the panacea I was hoping for. 🙂


      • Marc Dacey Sep 15, 2016, 12:27 am

        Eric, your mention of a spring starter intrigues me. Would you suggest that a good choice for a spare starter would be a spring starter? It seems to cover off the need for a spare and the possible failure of one’s electrical setup.

    • John Sep 14, 2016, 10:35 am

      Hi Chuck,

      I would agree 100% with Eric, keep it simple and go with a standard electrical starter motor. I also agree that any long distance voyaging boat should carry a spare starter motor. I have had two fail on me over the years and both times I had a spare, so the fix took less than an hour.

      The other advantage with electrical starter motors is that they can generally be repaired or rewound by any decent electrical shop.

      • Chuck B Sep 14, 2016, 10:56 am

        Thank you John. There’s an additional advantage that electrical starters are substantially cheaper! Just means battery, wiring, charging isolation, etc.


  • Terje M Sep 22, 2016, 10:00 am


    When I charge the batteries I always charge too minimum 85%. Normally I charge all the way up. I never ever discharge the batteries below 50%. When around 65-70% I normally start thinking of getting more charge into them.

    I was originally sceptical to big black boxes doing everything. I normally go for one unit per operation. With my Struder – it is different. First of all, it has never missed a tick. Second I know the UK reseller very well. Rob was one of the first starting using this unit in a marine environment, and done so for many years. According to him the unit have never failed any of his many marine customers. It is remarkable, other brands got a % fail rate. The Struder just keeps on going. It is used in the most extreme environments, North Pole, high up in the mountains with extreme frost and snow. Salt, sea and damp conditions is a killer for any electronic component. This unit is doing remarkable well.

    If it fails one day, I more likely need to replace the box. That is a calculated risk I took. If that happens I know for fact that the manufacture in Switzerland want me to send the unit to them for investigation. They are that supportive of their product.

    The batteries and charger systems are now almost 6 years old. The boat is used hard, without being a live-on-board boat.
    Yacht Maud

    • John Sep 22, 2016, 8:28 pm

      Hi Terje,

      As I said, sounds like a great unit. All I wanted to make clear was that it’s not going to fix sulphation.

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